Williams, who has won 15 Grand Slam singles titles and four Olympic gold medals, was 48-2 over the final seven months of the season.
It is the fourth time Williams has won the award, which is voted on by international tennis media. She also was named Player of the Year in 2002, 2008 and 2009.
Only Steffi Graf (eight times) and Martina Navratilova (seven times) have won the award more than Williams.
By John Solomon
How the government's punishing of the exposure of official wrongdoing can linger for years
Independent voices from the TWT Communities
A collection of reader guest articles, thoughts and opinions by Communities writers and breaking news and information.
Great discoveries in the world of restaurants and chefs fulfill the quest for delicious food and cooking.
Paul Rondeau dissects the propaganda, media tricks, and other shenanigans targeting our families, faith, and freedom…and even life itself
Benghazi: The anatomy of a scandal
Vietnam Memorial adds four names
Cinco de Mayo on the Mall
NRA kicks off annual convention